Plk1 belongs to a small family of protein kinases characterized by a phosphoserine/threonine binding domain known as the polo box domain. Plk1 plays a central role in the regulation of the cell cycle. Among other functions, Plk1 is thought to regulate initiation, progression, and exit from mitosis, the stage when cancer cells divide. Consequently, blocking Plk1 in cancer cells prevents their division or mitosis.
Potent anticancer agents have been identified that interfere with mitosis such as the vinca alkaloids (NAVELBINE®), taxoids (TAXOTERE®) and topoisomerase II inhibitors (ADRIAMYCIN®). VELCADE® is an antineoplastic agent that inhibits the 26S proteosome. However, these drugs cause considerable side effects upon normal, non-dividing cells. Plk inhibitors specifically target dividing cells and may be able to avoid the undesirable toxicities.
Inhibitors of Plk1 are known in the art. See for example, WO 06/066172. Additionally, WO 06/021548 discloses certain dihydropteridinone analogs (e.g., BI-2536) as inhibitors of Plk1. Currently, BI-2536 is in phase II clinical trials but has high clearance (CL >1000 mL/min) and is dose limited by myelosupression in man. There is still a need for further compounds that inhibit Plk1 which possess improved potency or pharmacokinetic properties. It would also be advantageous to have a Plk1 inhibitor that could be dosed orally.
The present invention provides novel imidazolidinonyl aminopyrimidine compounds believed to have clinical use for treatment of cancer through inhibiting Plk1. Certain of these compounds are believed to have improved potency over compounds disclosed in WO 06/066172. Additionally, certain of these compounds are believed to have improved pharmacokinetic properties over BI-2536. Further, due to the oral bioavailability of the compounds of the present invention that were tested, it is believed that certain of these compounds could be dosed orally.